Steam cracking has long been used to crack various hydrocarbon feedstocks into olefins. Conventional steam cracking utilizes a pyrolysis furnace having two primary sections: a convection section and a radiant section. The hydrocarbon feedstock typically enters the convection section of the furnace as a liquid (except for light feedstocks that enter as a vapor), wherein it is typically heated and vaporized by indirect contact with hot flue gas from the radiant section and by direct contact with steam. The vaporized feedstock and steam mixture is then introduced into the radiant section where the cracking takes place. The resulting cracked products, including olefins, leave the pyrolysis furnace for further downstream processing, such as quenching.
Hydrocarbon feedstocks to be cracked may come from a variety of internal and external sources and typically differ in composition. Crude petroleum feedstocks also differ in composition. Inconsistency in composition between multiple feedstocks can result in incompatibility and precipitation, particularly of asphaltenes.
Asphaltene precipitation can result in the deposition of organic solids, such as foulant and coke, on equipment such as refinery process equipment that contact the oil. Even small amounts of foulant or coke on equipment surfaces can result in energy loss because of fouled heat transfer surfaces. Moderate fouling can cause high pressure drop and interfere with and/or make equipment operation inefficient. Significant fouling may plug up equipment, which may prevent or impede flow and require equipment to be shut down and cleaned.
It would be desirable to have a process for cracking hydrocarbon feedstocks in which the incidence of asphaltene precipitation is substantially reduced or eliminated.